1. Field of the Invention
This invention relates to an engine lubricating system and has particular applicability to a fuel injected two cycle engine.
2. Description of the Related Art
Two cycle internal combustion engines are typically lubricated by supplying lubricant through the engine's induction and porting system for lubricating the various moving components of the engine. Lubricant can be supplied in a wide variety of manners. For example, lubricant may be mixed with fuel, may be sprayed into the induction system of the engine, may be delivered directly to certain components of the engine, or may be supplied by any combination of the above.
In conventional two cycle engines, air from an air intake system travels through reed valves into a crank chamber of the engine. Air from the crank chamber is supplied to the cylinders for combustion. Typically, fuel such as gasoline is mixed with lubrication oil and supplied to the air flow on an upstream side of the reed valves. The viscosity of this fuel/lubricant mixture is low in comparison with a typical lubricant taken alone. Because of its low viscosity, the mixture is easily sprayed and distributed to various parts of the engine for lubrication.
In order to reduce unburned hydrocarbons and engine exhaust emissions, many internal combustion engines now employ direct fuel injection, wherein the fuel is directly injected into the cylinders. In these engine arrangements, the fuel is not mixed with lubricant. As a result, the viscosity of the lubricant is increased and the lubricant is not smoothly sprayed and distributed. Due to its heavy viscosity, when lubricant is supplied upstream of the reed valves, lubricant particles tend to stick together when passing through the valves. The large particles increase lubricant inconsistency, possibly preventing even distribution of lubricant over the engine components.
Lubricant in the crankcase chamber is distributed to the various components of the engine, for instance the pistons and cylinder areas. In two cycle engines, lubricant also typically flows into the scavenging passages. At least some of the lubricant that collects in the scavenge passages may flow into a cylinder combustion chamber and be at least partially burned. Invasion of oil into the combustion chamber at least partially defeats the purpose of fuel injection by contributing additional hydrocarbon exhaust emissions, which direct fuel injection is intended to reduce.
In outboard motor applications, the engine is normally positioned with its cylinders extending horizontally and crankshaft rotating about a vertically extending axis. As is typical with two cycle engines, each crankcase chamber is sealed from the other. However, the seals may permit some leakage from the uppermost crankcase chamber to the lowermost chamber and lubricant may tend to collect in the lowermost portions of the engine. This can cause inadequate lubrication in the uppermost portions and oil overflow in the lower portions. Performance of the engine is decreased.